Answer

It is difficult to give a clear answer at this stage; it is quite likely that ther will be a need for some fom of export customs declaration for goods being supplied to EU clients, but the exact nature of this will depend on the negotiations. Currently many UK organisations involved in export shipping and customs are lobbying govenment and HMRC for a softer, solution which will minimise the impact of changes and the administrative & cost burden on traders and HM RC.

It is possible that a new form of certificate of origin will be introduced after Brexit (Switzerland has its own format of C/O). Its use will depend on the outcome of the negotiations.